This application claims priority to Japanese Patent Application Nos. 2001-287082 filed on Sep. 20, 2001 and 2002-270563 filed on Sep. 17, 2002.
The present invention relates to a metal filling method and member with filled metal sections in which a metal is filled into fine holes formed in a member, such as through holes or non-through holes formed in a circuit substrate.
For example, in the case of forming through hole electrodes (via hole electrodes) in a substrate (such as a silicon substrate) in the production process of an IC chip and so forth, a plating method is typically used in which through holes for the through hole electrodes are opened in the substrate, the substrate is inserted into a plating solution (molten metal) in which a conductive metal has been solved, and immersed in that the plating solution to fill the into the conductive metal through holes.
However, in the case of filling metal into through holes by the plating method, there are cases in which, for some reason, the plating layer concentrically grow near the through hole entrance of the substrate, thereby making it difficult for plating liquid to enter to the back of the through holes. In this case, there are problems such as the occurrence of roughness within the through holes that made it difficult to fill metal in a state free of voids.
In cases in which the through holes are fine holes having a high aspect ratio (depth of the hole/opening diameter of the hole) in particular, since it is difficult for the plating solution to penetrate to the back of the through holes, concentrated growth of the plating layer near the through hole entrance of the substrate occurs easily, causing the problems described above to become remarkable. For example, in the case of high-density, three-dimensional mounting consisting of the stacking of silicon IC chips and so forth, although there are cases in which through electrodes (through wirings) are formed in the substrate for connecting the wiring patterns on the top and bottom of a substrate, since the through holes for through electrodes opened in the substrate are fine holes having a high aspect ratio, if through electrodes are attempted to be formed by filling metal into the through holes using the plating method described above, it is difficult to reliably form through electrodes that are free of voids.
In consideration of the above problems, the object of the present invention is to provide a metal filling method and member with filled metal sections that allows filling of a plating solution to be carried out reliably particularly near openings that open on the outer surface of a work piece of fine holes formed in that work piece.
The metal filling method according to the present invention is a method for filling metal into fine holes formed in a work piece, and is characterized by forming a metal layer on the inner surface of an end of each fine hole that opens in an outer surface of the work piece, followed by immersing the work piece in the plating solution, filling the plating solution into the fine holes, removing the work piece from the plating solution with one of ends along an axial direction of each fine hole still occluded, and then cooling the work piece.
In this metal filling method, a constitution can also be employed in which the fine holes are through holes that pass through the work piece, the metal layer is formed on the inner surface of at least one end of both ends in the axial direction of each through hole, and when the work piece, which has been immersed in the plating solution to fill the plating solution into the through holes, is removed from the plating solution, an opening in the other end of the axial direction of each through holes is occluded with a sealing material as the above one of ends along the axial direction of each fine hole. Moreover, the metal layer can be formed on the inner surface of the end of the fine hole that opens in the outer surface of the work piece as well as on the outer surface of the work piece extending around the end of the fine hole on which the metal layer is formed. In this case, after immersing this work piece in the plating solution within a plating solution bath to fill the plating solution into the fine hole but prior to cooling of the work piece, the plating solution filled into the fine hole is padded at the sites where the metal layer was formed on the inner surface of the end of the fine hole that opens on the outer surface of the work piece and on the outer surface of the work piece extending around the end of the fine hole on the work piece which is removed from the plating solution. And then, a filled metal section formed by solidification of the plating solution within the fine holes, and an external metal section formed by solidification of the padded sections of the plating solution, are formed unitarily by cooling said work piece.
In addition, in the metal filling method as claimed in the present invention, the metal layer around the openings of fine holes in the outer surface of a work piece can also be patterned corresponding to the shape of the external metal sections to be formed prior to immersing the work piece in the plating solution.
The member with filled metal sections according to the present invention is a member with filled metal sections having filled metal sections formed by filling a metal into fine holes formed in a work piece, and is characterized by a metal layer being formed on the inner surface of an end of the above fine holes that opens to the outer surface of the work piece, and the filled metal sections being filled at a site that includes the end of the fine holes on which the above metal layer is formed. A constitution can also be employed for this member with filled metal sections in which a metal layer is formed not only on the inner surface of the end of the fine holes that opens in the outer surface of the work piece, but also on the outer surface of the work piece that extends around the end of the fine holes on which the metal layer is formed, and external metal sections, which are unitarily formed with the filled metal sections, and padded so as to protrude from the outer surface of the work piece, are formed so as to cover the metal layer.
The work piece as claimed in this invention is a member having fine holes for metal filling that are either through holes (fine holes) or non-through holes (fine holes in which only one end in the axial direction open on the outer surface of the work piece, while the other end are not open), examples of which include a substrate (circuit substrate) in which via holes or so-called inner via holes are formed. In addition to semiconductor materials such as silicon or gallium arsenide (GaAs), various other materials such as glass or other insulating material can be used for the material of the work piece.
Examples of methods for forming fine holes (through holes or non-through holes) in the work piece as claimed in the present invention include Deep-Reactive Etching (DRIE) as is represented by Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE), wet etching methods using an etching solution, mechanical processing methods using a microdrill, and optical excitation electrolytic polishing. Fine hole diameter, work piece dimensions, fine hole depth and so forth are suitably set according to the application and so forth, and the cross-sectional shape of the fine holes (shape of the cross-section perpendicular to the axial direction) may be of any shape such as circular, oval, triangular or rectangular (including a square).
In the metal filling method as claimed in the present invention, a technique is employed in which, after immersing a work piece in a plating solution which is composed of heated and melted conductive metal and filling this plating solution into the fine holes by allowing a plating solution to flow into the fine holes, the work piece is removed from the plating solution with one of the ends in the axial direction of the above fine holes still occluded, after which the work piece is cooled to solidify the plating solution in the fine holes. In the case the fine holes are through holes, through wirings and so forth can be formed by solidifying the plating solution that has been filled into the fine holes of the work piece, and in the case the fine holes are non-through holes, internal electrodes, internal wirings and so forth can be formed in the form of filled metal sections by the solidified conductive metal.
Furthermore, when removing the work piece from the plating solution, having one of the ends in the axial direction of the fine holes still occluded can be realized by covering one of the ends along the axial direction of each through hole using a sealing material in the case the fine holes are through holes. In addition, in the case the fine holes are non-through holes, since the constitution of the non-through hole itself is such that one end along the axial direction is open while the other end is blocked, it goes without saying that the use of a sealing material is not required.
In the metal filling method as claimed in the present invention, since the heated and melted conductive metal is filled into fine holes, defective filling caused by concentrated growth of the plating layer at the entrance of fine holes in the case of a plating method (including the formation of voids as previously described) can be avoided. In the present invention, xe2x80x9cplating solutionxe2x80x9d refers to this heated and melted conductive metal.
In the present invention, immersion of the work piece into the plating solution refers to submerging the work piece in the plating solution, or in other words, the work piece is inserted into the plating solution. However, the immersion referred to here is not limited to the immersion of the work piece into the plating solution stored in a bath (to also be referred to as a plating solution bath), but also includes the injection of the plating solution into a container that houses the work piece (including the above plating solution bath). Here, xe2x80x9cfillingxe2x80x9d into fine holes is not limited to filling entire fine pores without voids, and a constitution in which, for example, voids are left in a portion of the fine holes in the axial direction (case of filling metal into inner via holes or other non-through holes) or a slight amount of space is present in the filled metal, is also included. In the present invention, as a result of being able to reliably fill metal near the entrance of the openings of the fine holes in particular, the electrical and mechanical properties of the filled metal sections can be adequately secured. In addition, xe2x80x9cremovalxe2x80x9d of the work piece from the plating solution includes lifting up the work piece from out of the plating solution retained in a bath, removing the work piece in the horizontal direction, and exposing a work piece that has been immersed in the plating solution in a bath by discharging the plating solution from inside the bath.
However, as a result of the inventors of the present invention verifying the filled status of the plating solution within fine holes after removing a work piece in the form of a substrate formed from silicon and glass from the plating solution, merely a method is used in which a work piece in which the plating solution has flown into and filled fine holes is simply lifted out (equivalent to xe2x80x9cremovedxe2x80x9d) from the plating solution with the closed side among both ends in the axial direction of each fine hole is the lower end, it was found that, as a result of it being easy for the plating solution to flow out from the opening of each fine holes that opens on the upper surface during removal of the work piece, and the plating solution flowing out during removal, there are many cases in which there is insufficient filling of the plating solution during cooling and solidification. Since the amount of the plating solution contained in the fine holes decreases if outflow of the plating solution occurs, as shown in FIG. 15, for example, the upper surface of the plating solution 2 within each fine hole 1 (through holes are shown in FIG. 15) ends up being slightly lower than the upper surface 4 of work piece 3 (a substrate in FIG. 15), resulting in the formation of level difference D. In addition, if this level difference is formed as shown in FIG. 15, even if, for example, bumps are attempted to be formed and bonded in a separate step on through wirings in which the plating solution has solidified, there is susceptibility to the occurrence of bonding defects between the bumps and through wirings, which can easily become a cause of defects such as incomplete electrical connections.
The phenomenon in which the plating solution flows out from the fine holes during removal of the work piece from the plating solution is caused by being unable to ensure adequate wettability with the plating solution in the case of using silicon and glass to form the work piece. That is, since there is a lack of acclimation between the inner surfaces of the fine holes and the plating solution, outflow of the plating solution from the fine holes occurs easily.
In the present invention, wettability with the plating solution that has been filled into fine holes is ensured by a metal layer formed on the inner surface of the end of each fine hole that is an upper end when the work piece is removed (by being lifted out and so forth) from the plating solution. As a result, when the work piece is removed from the plating solution, it is difficult for the plating solution to flow out from the openings of the fine holes, thereby being able to prevent problems such as the formation of a level difference near the openings of the fine holes. The metal layer is preferably formed over as a broad range as possible on the inner surface near the entrance of each fine hole. In the case the fine holes are through holes, if a metal layer is formed on the inner surface of both ends of each through hole, even if the metal layer is not formed over the entire inner surface along the lengthwise direction in the axial direction of the through hole, the plating solution is effectively acclimated throughout the entire through hole, thereby being effective in preventing the formation of voids and so forth within the through hole.
If a metal layer is formed on the inner surface of the end of each fine hole that opens to the outer surface of the work piece, as well as on the outer surface of the work piece that extends around the end of the fine hole, the outflow of the plating solution from the fine holes when the substrate is removed from the plating solution can be more reliably prevented due to the wettability of the plating solution with respect to the metal layer surrounding the openings. In addition, when the work piece is removed from the plating solution, by taking advantage of the formation of a layer of the conductive metal along this metal layer (metal layer around the openings), grounded sections, bumps and other external metal sections of the wiring can be formed on the substrate by cooling and solidifying the plating solution on this metal layer. Here, grounded sections, bumps and other external metal sections that are formed refer to those for which the plating solution is cooled and solidified after having been padded at those sites where the metal layer formed around the openings of the fine hole is present, and are unitarily formed with the filled metal sections that are solidified within the fine hole. Since the grounded sections, bumps and other external metal sections that are formed are continuous with the filled metal sections by the same type of metal as the filled metal sections, in comparison with the case of forming separately from the filled metal sections, there is the advantage of the absence of problems such as defective bonding with the filled metal sections. In addition, there are also no problems such as brittleness of the bonded sections (bonded sections between external metal sections and filled metal sections) caused by differences in the coefficients of thermal expansion or diffusion of materials and so forth that occur in the case the external metal sections and filled metal sections are of different types of materials.
For example, in the case of forming external metal sections in the form of bumps on the work piece in the form of the substrate, the size, shape and so forth can be adjusted according to the range of formation and so forth of the metal layer around the opening of each fine hole on one side of the substrate. When the substrate is removed from the plating solution, since the plating solution that remains at the sites where the metal layer is present that is formed at the opening of each fine hole and around the openings on one side of the substrate can be padded in a peak-shape due to its surface tension and so forth, a peak-shaped bump can be obtained by solidifying the plating solution. Thus, the height, size and so forth of bumps can be adjusted by adjusting the formation range of the metal layer around the openings of fine holes on one side of the substrate by patterning or other means.
In the member with filled metal sections as claimed in the present invention, since superior adherence is ensured between a metal layer and a filled metal section which is filled into the end of each fine hole on which a metal layer is formed due to the wettability of the metal layer formed on the inside of the end of fine hole that opens to the outer surface of the work piece, the fixed state of the filled metal section near the end of the fine hole can be maintained with stability over a long period of time, and since peeling of the filled metal section from the inner surface of the fine hole and lifting of the filled metal section within the fine hole can be reliably prevented, long-term stability is obtained.
Moreover, in a constitution in which an external metal section unitarily formed with the above filled metal section and padded so as to protrude beyond the outer surface of the work piece is formed so as to cover the metal layer which is formed on the outer surface of the work piece and extends around the end of the fine hole on which the metal layer is formed, since the filled metal section within the fine hole and the external metal section can be formed unitarily, there is no occurrence of problems such as defective bonding due to bonding of different types of metals or brittleness of bonded sections caused by difference in the coefficients of thermal expansion, diffusion of materials, etc.
According to the present invention, wettability with the plating solution filled into fine holes is ensured by the metal layer formed on the inner surface of the end that opens to the outer surface of a work piece among both ends of each fine hole. As a result, when a substrate is removed from the plating solution, it is difficult for the plating solution to flow out from the opening of the fine hole, and problems can be prevented such as the formation of a level difference near the opening of the fine hole. If this level difference is eliminated, bonding can be carried out reliably in the case of bonding bumps and so forth formed in a separate step to filled metal sections of through wirings and so forth in which this plating solution has solidified, thereby allowing bonding defects to be prevented. In addition, if a metal layer is formed on the inner surface of the end of the fine hole that opens to the outer surface of a work piece, the formation of voids inside the fine hole (and especially voids that form easily near the occluded end when the work piece is immersed in the plating solution) can be effectively prevented, thereby enabling the plating solution to be reliably filled throughout the fine hole and allowing the formation of reliable through wirings free of level differences and voids.
As a result of forming the metal layer on the inner surface near the opening of each fine hole and around the opening of the fine hole on the outer surface of the work piece, the outflow of the plating solution from the fine hole when the work piece is removed from the plating solution can be more reliably prevented due to the wettability of the plating solution with respect to the metal layer around the opening. In addition, when a substrate is removed from the plating solution, by taking advantage of the formation of a layer of the conductive metal along this metal layer (metal layer around the opening), wiring grounded sections, bumps and so forth can be formed on the substrate by cooling and solidifying the plating solution on this metal layer.
If the above external metal section is formed by cooling and solidifying the plating solution that is continuous with the fine hole and has been padded at those locations where the metal layer is present that has been formed in the opening of each fine hole in the outer surface of the work piece as well as around the opening, since this external metal section is formed unitarily with filled metal section formed by the plating solution that solidifies within the fine hole, there is the advantage of the absence of defective bonding and so forth with the filled metal section. In addition, there are also no problems such as brittleness of a bonded section (bonded section between the external metal section and filled metal section) caused by differences in coefficients of thermal expansion or diffusion of materials like those which occur in the case of the external metal section and filled metal section being of different materials, thereby resulting in improved long-term reliability.
In the formation of the metal layer around the opening of each fine hole in the outer surface of the work piece, bumps and so forth of a target size can be formed easily by patterning the metal layer according to the target shape of the external metal portions (such as bumps) to be formed. In this case, the range of formation of the metal layer around the opening of the fine hole in outer surface of the work piece can be adjusted by patterning, offering the advantage of being able to easily adjust the height, size and so forth of the bumps.